The invention relates to TPU compositions with good flame retardancy as well as such TPU compositions that also include electrostatic dissipative polymers, an in addition good clarity and/or transparency.
It is generally very challenging to improve the flame retardancy of TPU compositions. This is because TPU materials typically de-polymerize into more flammable lower molecular weight monomers when exposed to high heat levels, which leads to dripping and smoke generation. Effective non-halogenated flame retardants are especially limited. While a liquid flame retardant additive can be added to a TPU composition, they generally cause dramatic increases in the smoke density seen from the composition when exposed to fire-like conditions. When traditional solid flame retardants are used, the clarity of the resulting TPU composition, which is required for some applications, is often harmed and even completely lost.
There is a desire for a TPU composition with improved flame retardancy, and specifically improved performance in the ASTM E84 Class I and UL94 V0 ratings procedures. It is most desirable to achieve these improved results without the use of a halogenated flame retardant additive, or any flame retardant additive at all. There is also a desire for such TPU compositions that are also translucent and/or transparent. There is also a desire for such TPU compositions that are also inherently dissipative with regards to electrostatic charges. Combining materials with good flame retardancy with materials with good electrostatic properties results in a blend that has diminished effectiveness in one or both of these areas. It is very difficult to maintain the desired properties of the materials and end up with a final composition that has good performance in both areas. Clarity and transparency adds yet another difficulty and combining materials, even when each is clear on their own, often results in a blend that has reduced clarity. There is a need for compositions that balance all of these properties resulting in materials with good flame retardancy, good electrostatic properties, and good clarity.